Damp proofing or a Damp-Proof in construction is a type of moisture control applied to building walls and floors to prevent moisture from passing into the interior spaces. Dampness problems are among the most frequent problems encountered in residences. Damp proofing is defined by the American Society for Testing and Materials (ASTM) as a material that resists the passage of water with no hydrostatic pressure. Waterproof is defined by the ASTM as a treatment that resists the passage of water under pressure. 

Generally, damp proofing keeps moisture out of a building, where vapor barriers keep interior moisture from getting into walls. Moisture resistance is not necessarily absolute; it is usually defined by a specific test method, limits, and engineering tolerances.